Apple’s Podcast app may or may not support subscribing to a subscription podcast feed such as the Genealogy Gems Premium Podcast.
Premium podcast feed: itpc://lisalouisecooke.com/Premium_Feed/feed.xml
If subscribing is unsuccessful, you can try downloading the Downcast app from the Mac App Store here. You will need to manually add the Premium podcast feed (above) and then sign in with your Genealogy Gems Premium membership user name and password.